In such circuits, it is often required to define several triggering thresholds, for example, to create various devices of protection against electrostatic discharges, battery inversions, or others.
Generally, as shown in FIG. 1, an avalanche diode is made by forming in a substrate 1 of a first conductivity type a region 2 of the opposite conductivity type. It should be noted that "substrate" is here used to designate a region or upper layer of a semiconductor component, for example, an integrated circuit. Region 2 generally is heavily doped and the breakdown threshold of the avalanche diode is essentially determined by the doping level of substrate 1 (the less the substrate is doped, the higher the breakdown voltage of the device).
FIG. 2 shows another example of an avalanche diode currently used in integrated circuits. In substrate 1 of the first conductivity type, a diffused (or implanted-diffused) region 3 of the same conductivity type is created. A region 2 of the opposite conductivity type is formed to laterally protrude from region 3 to obtain a breakdown independent from edge and surface effects. Assuming that substrate 1 of FIG. 2 is the same as that of FIG. 1, the avalanche voltage of junction 2-3, which depends on the doping level of region P, necessarily is lower than that of junction 2-1 since the concentration of region 3 at its junction with region 2 necessarily is higher than that of region 1.
Thus, generally, in any method of manufacturing of a semiconductor component or of an integrated circuit, the various types of diffusion provided for the manufacturing of other components of the integrated circuit can be used to form avalanche diodes. However, the breakdown thresholds of the various diodes are determined without any possible choice by the doping level of the existing regions and, in many simple lines of manufacturing of integrated circuits such as power integrated circuits, there are only the two possibilities, which are illustrated in FIGS. 1 and 2.
Thus, in an existing device, to obtain a diode with a specific avalanche threshold, a specific diffused region 3 should be provided, that is, a region with a specific implantation dose or a specific anneal duration. It is of course impossible in an integrated circuit to provide an area with a specific anneal duration since the anneal performed for this area would react upon the other areas of the integrated circuit. On the other hand, to perform this implantation at a specific dose would increase the number of integrated circuit manufacturing steps, which is always attempted to be avoided in an existing line.